共查询到20条相似文献,搜索用时 46 毫秒
1.
Marina Koledintseva James Drewniak James Lenn 《Journal of magnetism and magnetic materials》2009,321(7):730-733
An analytical model for a magneto-dielectric composite material is presented based on the Maxwell Garnett rule for a dielectric mixture, and on Bruggeman's effective medium theory for permeability of a ferrite powder embedded in a dielectric. In order to simultaneously treat frequency-dispersive permittivity and permeability of a composite in a full-wave FDTD code, a new algorithm based on discretized auxiliary differential equations has been implemented. In this paper, numerical examples of modeling structures containing different magneto-dielectric mixtures are presented. 相似文献
2.
Marina Y. Koledintseva Victor V. KhilkevichAlexander G. Razmadze Aleksandr G. GafarovSoumya De James L. Drewniak 《Journal of magnetism and magnetic materials》2012
An analytical model to evaluate attenuation on the coaxial line with the central conductor coated with a magneto-dielectric layer is proposed and validated by the experiments and numerical modeling. This model is convenient for comparing absorptive effectiveness of different materials, as well as of different thicknesses and lengths of the same material. The proposed model also lays the basis for the technique to extract permeability of thin sheet magneto-dielectric materials by wrapping them around a central conductor of the coaxial airline. 相似文献
3.
We study numerically rigorous dispersion relations for a plane-parallel waveguide in which the impedance of the walls is determined
as either the impedance of a multilayer magneto-dielectric wall having a finite thickness, or as the impedance of a corresponding
finite or infinite layer. Solutions for complex waves are obtained on the basis of the numerical iterative method. The corresponding
analytical relationships are found in some limiting cases. 相似文献
4.
Sound propagation in inhomogeneous waveguides with sound-speed profiles using the multimodal admittance method
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《中国物理 B》2020,(1)
The multimodal admittance method and its improvement are presented to deal with various aspects in underwater acoustics, mostly for the sound propagation in inhomogeneous waveguides with sound-speed profiles, arbitrary-shaped liquid-like scatterers, and range-dependent environments. In all cases, the propagation problem governed by the Helmholtz equation is transformed into initial value problems of two coupled first-order evolution equations with respect to the modal components of field quantities(sound pressure and its derivative), by projecting the Helmholtz equation on a constructed orthogonal and complete local basis. The admittance matrix, which is the modal representation of Direchlet-to-Neumann operator, is introduced to compute the first-order evolution equations with no numerical instability caused by evanescent modes. The fourth-order Magnus scheme is used for the numerical integration of differential equations in the numerical implementation. The numerical experiments of sound field in underwater inhomogeneous waveguides generated by point sources are performed. Besides, the numerical results computed by simulation software COMSOL Multiphysics are given to validate the correction of the multimodal admittance method. It is shown that the multimodal admittance method is an efficient and stable numerical method to solve the wave propagation problem in inhomogeneous underwater waveguides with sound-speed profiles, liquid-like scatterers, and range-dependent environments. The extension of the method to more complicated waveguides such as horizontally stratified waveguides is available. 相似文献
5.
Adrian Doicu Thomas Wriedt 《Journal of Quantitative Spectroscopy & Radiative Transfer》2001,70(4-6):663-673
We describe a T-matrix program for light scattering calculations from particles with complex structure. The code treats the cases of homogeneous, layered and composite scatterers. These results are combined with basic results concerning the scattering by inhomogeneous scatterers and aggregates to apply to more general types of scatterers. Some numerical simulations are presented. 相似文献
6.
Didier Felbacq 《Photonics and Nanostructures》2013,11(4):436-441
The homogenization of a metamaterial made of a collection of scatterers periodically disposed is studied from an asymptotic theory and an optimization algorithm. Detailed numerical results are given for resonant scatterers and the spatial dispersion is investigated. 相似文献
7.
We present a method for numerical wave propagation in a heterogeneous medium. The medium is defined in terms of an extended scatterer or target which is surrounded by many small scatterers. By extending the classic Foldy-Lax formulation we developed an efficient algorithm for numerical wave propagation in two dimension. In the method that we set forth multiple scattering among the point scatterers and the extended target is fully taken into account via a boundary integral formulation coupled with the Foldy-Lax formulation. This formulation forms the basis for our numerical procedure. 相似文献
8.
V. A. Burov E. E. Kasatkina A. Yu. Poberezhskaya A. V. Bogatyrev O. D. Rumyantseva 《Acoustical Physics》2011,57(5):681-695
A direct problem of scattering for refractive-absorbing scatterers of different shapes and strengths is considered. A rigorous
solution for two- and three-dimensional problems and its numerical implementation are obtained on the basis of equations of
the Lippmann-Schwinger type in the coordinate space and in the space of special frequencies that is Fourier-conjugate to it.
Attention is given to selection of parameters for problem sampling that are fundamentally important for providing adequacy
of numerical simulation. Techniques for restricting the Green’s function support and introducing a reserve band are used.
The results of numerical calculation for wave fields and secondary sources are given for different scatterers. The major laws
connected with the effects of sound wave rescattering are illustrated and discussed. 相似文献
9.
《Waves in Random and Complex Media》2013,23(4):653-697
We consider a heterogeneous magneto-dielectric photonic crystal and derive the so-called ‘homogenized Maxwell system’ via the multi-scale method and provide ad hoc proofs for the convergence of the electromagnetic field towards the homogeneous one using the notion of two-scale convergence. The homogenized medium is described by anisotropic matrices of permittivity and permeability, deduced from the resolution of two annex problems of electrostatic type on a periodic cell. Noteworthily, this asymptotic analysis also covers the case of photonic crystals with non-cuboidal periodic cells. We solve numerically the associated system of partial differential equations with a method of fictitious charges and a finite element method (FEM) in order to exhibit the matrices of effective permittivity and permeability for given magneto-dielectric periodic composites. We then compare our results in the 2D case against some Fourier expansion approach and provide duality relations in the case of magneto-dielectric checkerboards. We further compute some low-frequency eigenmodes of a photonic crystal fiber with metallic outer boundary and compare them with the eigenmodes of a corresponding effective anisotropic waveguide, thanks to the FEM. Finally, we derive the effective properties of a 3D photonic crystal both through classical homogenization (solving numerically two decoupled annex problems) and Bloch wave homogenization. In the case of spherical inclusions, the latter approach amounts to evaluating the slope of the first band around the origin on a Bloch diagram which we compute using finite edge elements. 相似文献
10.
The aim of this paper is to propose a numerical strategy for computing the solution of two-dimensional time-harmonic acoustic multiple scattering problems at high-frequency. The scatterers are assumed to be circular, leading therefore to semi-analytical representation formulae of the scattered field through the solution of a large linear system of equations. Taking advantage of the special block Toeplitz structure of the matrix of the linear system, a fast iterative and preconditioned numerical method yielding large memory savings is proposed. Several numerical experiments for general configurations are presented to show the efficiency of the numerical method. 相似文献
11.
Y. Asada A. Freyn J.-L. Pichard 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,53(1):109-120
A nano-system in which electrons interact and in contact with
Fermi leads gives rise to an effective one-body scattering which
depends on the presence of other scatterers in the attached leads.
This non local effect is a pure many-body effect that one neglects
when one takes non interacting models for describing quantum transport.
This enhances the non-local character of the quantum conductance by
exchange interactions of a type similar to the RKKY-interaction between
local magnetic moments. A theoretical study of this effect is given
assuming the Hartree-Fock approximation for spinless fermions of Fermi
momentum kF in an infinite chain embedding two scatterers
separated by a segment of length Lc. The fermions interact only inside
the two scatterers. The dependence of one scatterer onto the other exhibits
oscillations of period π/kF which decay as 1/Lc and
which are suppressed when Lc exceeds the thermal length
LT. The analytical results given by the Hartree-Fock
approximation are compared with exact numerical results obtained with
the embedding method and the DMRG algorithm. 相似文献
12.
Motivated by recent graphene transport experiments, we undertake a numerical study of the conductivity of disordered two-dimensional massless Dirac fermions. Our results reveal distinct differences between the cases of short-range and Coulomb randomly distributed scatterers. We speculate that this behavior is related to the Boltzmann transport theory prediction of dirty-limit behavior for Coulomb scatterers. 相似文献
13.
14.
A novel formulation for improving the numerical stability of the null-field method for highly elongated and flattened composite scatterers is presented. The key step in this approach is to approximate the surface current densities by the lowest-order multipoles located in the complex plane. The accuracy of the proposed method is investigated from a numerical point of view. 相似文献
15.
Tian-Xue Ma Yue-Sheng Wang Xiao-Xing Su Yan-Feng Wang 《Physica B: Condensed Matter》2012,407(21):4186-4192
In this paper, the elastic band structures of two-dimensional solid phononic crystals (PCs) with both negative and positive Poisson's ratios are investigated based on the finite difference domain method. Systems with different combinations of mass density ratio and shear modulus ratio, filling fractions and lattices are considered. The numerical results show that for the PCs with both large mass density ratio and shear modulus ratio, the first bandgap becomes narrower with its upper edge becoming lower as Poisson's ratio of the scatterers decreases from −0.1 to −0.9. Generally, introducing the material with a negative Poisson's ratio for scatterers will make this bandgap lower and narrower. For the PCs with large mass density ratio and small shear modulus ratio, the first bandgap becomes wider with Poisson's ratio of the scatterers decreasing and that of the host increasing. It is easy to obtain a wide low-frequency bandgap by embedding scatterers with a negative Poisson's ratio into the host with a positive Poisson's ratio. The PCs with large filling fractions are more sensitive to the variations of Poisson's ratios. Use of negative Poisson's ratio provides us a way of tuning bandgaps. 相似文献
16.
Coherent backscattering of light by complex random media of spherical scatterers: numerical solution
Karri Muinonen 《Waves in Random and Complex Media》2004,14(3):365-388
Novel Monte Carlo techniques are described for the computation of reflection coefficient matrices for multiple scattering of light in plane-parallel random media of spherical scatterers. The present multiple scattering theory is composed of coherent backscattering and radiative transfer. In the radiative transfer part, the Stokes parameters of light escaping from the medium are updated at each scattering process in predefined angles of emergence. The scattering directions at each process are randomized using probability densities for the polar and azimuthal scattering angles: the former angle is generated using the single-scattering phase function, whereafter the latter follows from Kepler's equation. For spherical scatterers in the Rayleigh regime, randomization proceeds semi-analytically whereas, beyond that regime, cubic spline presentation of the scattering matrix is used for numerical computations. In the coherent backscattering part, the reciprocity of electromagnetic waves in the backscattering direction allows the renormalization of the reversely propagating waves, whereafter the scattering characteristics are computed in other directions. High orders of scattering (~10 000) can be treated because of the peculiar polarization characteristics of the reverse wave: after a number of scatterings, the polarization state of the reverse wave becomes independent of that of the incident wave, that is, it becomes fully dictated by the scatterings at the end of the reverse path. The coherent backscattering part depends on the single-scattering albedo in a non-monotonous way, the most pronounced signatures showing up for absorbing scatterers. The numerical results compare favourably to the literature results for nonabsorbing spherical scatterers both in and beyond the Rayleigh regime. 相似文献
17.
Victor P. Tishkovets Michael I. Mishchenko 《Journal of Quantitative Spectroscopy & Radiative Transfer》2009,110(1-2):139-145
We describe an approximate method for the calculation of all characteristics of coherent backscattering for a homogeneous, semi-infinite particulate medium. The method allows one to transform a system of integral equations describing coherent backscattering exactly into a system of linear algebraic equations affording an efficient numerical solution. Comparisons of approximate theoretical results with experimental data as well as with benchmark numerical results for a medium composed of nonabsorbing Rayleigh scatterers have shown that the method can be expected to give a good accuracy. 相似文献
18.
The scattering efficiencies of hard and soft cylindrical scatterers are compared using the Novikov-Grinevich-Manakov functional algorithm designed to reconstruct two-dimensional scatterers. The existence of a rigid relationship between the amplitude and phase of the wave scattered by a quasi- point-like scatterer and by scatterers with small wave sizes in the form of a soft cylinder, a soft sphere, and an air bubble in a liquid is confirmed by numerical simulations. 相似文献
19.
Straightforward application of numerical modelling approaches to Photonic Band-Gap structures demands the use of fine meshes, notably finer that the size of a single scattering element, in order that high accuracy is achieved. However simulations employing sufficiently fine meshing to correctly represent the geometry of the scatterers lead to very long computational run-times and huge memory consumption. Such direct numerical approaches to PBG characterisation are only suited to the analysis of single unit cells or for benchmarking. In practice, the computational overheads significantly increase when one deals with an array of cells or when modelling the global behaviour of a large number of devices integrated on a single substrate. Therefore in order to model the macroscopic response of PBG structures the possibility of employing meshes of much larger size than the individual scattering elements has been explored. A suitable approach, initially developed for Electromagnetic Compatibility predictions, has been modified to permit modelling of Photonic Crystal Waveguides. The method provides second order accuracy and leaves a designer with the flexibility to discretise the entire problem space with an arbitrary number of scatterers per mesh cell. Results are first presented for small clusters of scatterers and subsequently for complete photonic structures. 相似文献
20.
对于不小于波长或可与波长相比的大粒子集合性的相干散射,要求严格求解多次散射的Maxwel方程。作者利用多个粒子多次散射的严格的T矩阵公式,发展了数值模似算法,求出非均匀群聚分布的球形粒子相干极化散射在全方位上的数值结果,研究了群聚粒子相干极化散射的特征表现,并与双球粒子散射的实验结果作了很好的比较。 相似文献